Mobile devices such as cellular phones typically receive an audio signal having a speech component and a noise component when used in most environments. Methods exist for processing the audio signal to identify and reduce a noise component within the audio signal. Sometimes, noise reduction techniques introduce distortion into the speech component of an audio signal. This distortion causes the desired speech signal to sound muffled and unnatural to a listener.
Currently, there is no way to identify the level of distortion created by a noise suppression system. The ITU-T G.160 standard teaches how to objectively measure Noise Suppression performance (SNRI, TNLR, DSN), and explicitly indicates that it does not measure Voice Quality or Voice Distortion. ITU-T P.835 subjectively measures Voice Quality with a Mean Opinion Score (MOS), but since the measure requires a survey of human listeners, the method is inefficient, expensive, time-consuming, and expensive. P.862 (PESQ) and various related tools attempt to automatically predict MOS scores, but only in the absence of noise and noise suppressors.